Ancient trade-off may explain why humans get HIV 19:00 21 June 2007 NewScientist.com news service Roxanne Khamsi A protein that protected our human ancestors against a virus that ravaged other primates may now be responsible for our susceptibility to HIV, a new study suggests. The discovery could help scientists predict which viruses found in other species are most likely to cross over and lethally infect humans. The idea that early humans had an immune system that differed from other primates first came about after biologists sequenced the chimp genome. The chimp sequence contains 130 copies of a virus called Pan...